The present invention relates to slotted substrates, used in microfluidic devices such as fluid ejection devices.
Generally, thermally actuated printheads use resistive or heating elements to achieve fluid or ink expulsion. A representative thermal inkjet printhead has a plurality of thin film resistors provided on a semiconductor substrate. A top layer defines firing chambers about each of the resistors. Propagation of a current or a xe2x80x9cfire signalxe2x80x9d through the resistor causes ink in a corresponding firing chamber to be heated and expelled through a corresponding nozzle.
In some printheads, fluid is routed to the firing chamber through a slot in the substrate. In some embodiments, the slot is formed while the substrate is part of a wafer die. Often, slots are formed in the wafer die by wet chemical etching of the substrate with, for example, Tetra Methyl Ammonium Hydroxide (TMAH) or potassium hydroxide (KOH). The etch rate for alkaline chemistries is different for different crystalline planes, and therefore the etch geometry is defined by the orientation of the crystalline planes. For example, on (100) substrates, TMAH etching techniques result in etch angles that cause a very wide backside slot opening. The wide backside opening limits how close the slots can be placed to each other on the die.
During processing, the substrate is often coated with masking films or layers that are substantially unaffected by the etchants. However, these films or layers are typically undercut as a result of extended etching time. Because of this, the etching time is often carefully monitored.
It is desired to efficiently etch slots in a die within certain dimensional tolerances, while maximizing the number of slots in the die.
In one embodiment, a method of manufacturing a slotted substrate includes forming a masking layer over a first surface of a substrate, and patterning and etching the masking layer to form a hole therethrough. The first layer is deposited over the masking layer and in the hole. The first layer is patterned and etched to form a plug in the hole. A second surface of the substrate that is opposite the first surface is continuously etched until a bottom surface of the plug is substantially exposed and a slot in the substrate is substantially formed.
Many of the attendant features of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts throughout.